1. Field of the Invention
This invention relates to lasers and particularly to a laser having an improved flashlamp cooling arrangement.
2. Description of the Prior Art
In order to produce laser action in an active laser, a certain minimum pump energy is required per unit volume of laser material above the minimum rate in order to sufficiently overcome spontaneous decay. The energy not utilized in excitation of the laser material takes the form of heat which, if not removed from the area surrounding the material, will cause deterioration of the laser action and flash lamp. In attempting to overcome the problem of heat buildup, several flashlamp cooling methods have been employed. Various techniques have been utilized such as using forced circulation of high pressure nitrogen or air and liquid cooling, for cooling both the flash lamp and laser material in one system. These methods are efficient but relatively cumbersome and expensive. The liquid system has limited coolant life, and tends to be relatively complex and inconvenient with regard to problems associated during flashlamp replacement. In addition, both the pressurized gas and liquid systems are usually designed so that the coolant path of the flashlamp and laser material are in series in order to prelude even greater bulkyness and complexity. This in turn requires that the overall series cooling system be designed to accommodate the relatively large heat load of the flashlamp, which can operate successfully at relatively high temperatures, with the relatively small allowable temperature rise of the laser material, which in turn introduces a relatively small amount of waste heat into the cooling system.
Other approaches that have been used to attempt to solve the problem of heat buildup has been the design of a new laser pump cavity configuration. The theory is that if substantial portions of the optical pump energy can be directed on the active laser element which has been made in the form of a rod, less pump energy will be wasted in the form of heating the pump cavity. An elliptical pump cavity configuration is one example of this, where the flash lamp is placed along one of the focal lines of the elliptical cylinder and the active laser element in the form of a rod which lies along the other focal line. This configuration provides good optical characteristics, but results in a large air space between the laser rod or the flashlamp and the cavity inner wall. When the laser is operated at a higher repetition rate, the laser element and the flashlamp become extremely hot and soon stop lasing due to the poor thermal path conducting the heat away from the laser rod and the flashlamp. Another example of this type of approach is placing of the flashlamp and the lasing rod in close proximity to each other surrounded by materials such as aluminum foil or magnesium oxide. The effect is not as efficient as the elliptical cavity. It does not supply an adequate heat sink and resulted in a high heat buildup in the laser rod and flashlamp.
Another method to overcome the heat problem is the Griest cavity shown in U.S. Pat. No. 3,475,697, and incorporating a semi-elliptical pump cavity. This arrangement focuses pump energy from a linear flashlamp on a laser rod that is in thermal contact with the heat sink. This method conducts heat well enough for low repetition rates but has been found to have a heat buildup for some lasers operating at very high repetition rates.